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A major challenge for biomedical science is developing materials and processing methods to enable creation of devices that can meaningfully translate signals between biology and electronics. Protonics-based devices—devices analogous to electronic devices but which use protons as charge carriers instead of electrons—are a promising strategy for such translation. Proton-conductive materials (PCMs)—the media through which protons are transported in such devices—are an element ripe for improvement, since they dominate the performance of protonic devices. We investigate protonic devices comprising sub-micrometer diameter, chitosan-fiber PCMs and palladium hydride (PdHx) protodes, the proton-injecting contact, to analyze how proton transport depends on the chemistry and ordering of the PCM. Current–voltage (I–V) measurements of single fiber-based devices under hydrogen atmospheres show that fibers electrospun from trifluoroacetic acid (TFA) solutions feature substantially higher proton conductivity, up to two orders of magnitude, compared to chitosan PCM films cast from acetic acid solutions. We further used digital simulation of the I–V data to elucidate the electrochemical and electrical processes that control device operation. The hydrogen oxidation reaction kinetics of the protode interfaces with the electrospun chitosan fibers agree well with those reported previously. Using X-ray photoelectron spectroscopy (XPS), we observed that single chitosan fibers spun from TFA solutions are more highly proton-doped than chitosan cast from acetic acid. Furthermore, I–V measurements on electrospun chitosan fibers vs. spin-cast chitosan films, both derived from TFA solutions, reveal that electrospun chitosan fibers yield ∼10-fold higher proton conductivity, suggesting that local polymer ordering within the electrospun fibers further enhances proton transport for chitosan PCMs. Finally, devices fabricated from single doped chitosan fibers behave as ionic field effect transistors (IFETs) when under a contact gate bias established with a conducting probe AFM tip. Switching characteristics are tuned by the gate bias, with proton conduction of a single fiber increasing by over an order of magnitude under negative bias. The switchable ion currents and enhanced conductivity of the chitosan fiber-based PCMs comprise a means of establishing spatiotemporal control over ionic communication between protonic devices and adjacent biological cells and membranes.

In bioelectronic medicine and electroceuticals, electronic devices that conduct electrons are used to monitor and control ion-based biochemical reactions in order to detect and treat medical conditions. Advancing these devices will require a thorough understanding of the electrochemical pathways that transduce electronic currents into the ionic currents that interact with the natural system. Here, we analyze the tranduction of electronic current into a protonic current (H+) using Pd/PdHx contacts and a model proton conductor, chitosan. Linear sweep voltammetry and electrochemical impedance spectroscopy data indicate that, for Pd, limited proton injection occurs at the interface aided by water oxidation. For PdHx, H desorption and electrochemical oxidation to H+ lead to sustainable proton injection and transfer to the chitosan protonic conductor. We have developed electroanalytical expressions and predictive digital simulations that match the experimental results. This work confirms that PdHx contacts integrated in DC devices, in parallel with electrochemical impedance spectroscopy, comprise a suitable means for measuring H+ currents and interrogating the proton conductivity in biomaterials.

We report several methods of chemical dehydrogenation of hydrogenated graphene (HG), characterizing the results using Raman, X-ray photoelectron spectroscopy, and electrical conductivity measurements. Notably, the hydrogen–graphene bonds appear to activate the graphene toward subsequent reaction such that, in several cases, the addition of the dehydrogenating agent to the graphene accompanies the removal of hydrogen. We compare the uptake of chemical groups on HG to those on pristine graphene and find that HG reacts more readily than pristine graphene with radical generators such as chlorine and AIBN.

We report systematically tuning the mechanical properties of vertical graphene (VG) sheets through fluorination. VG sheets were synthesized using a radio-frequency plasma-enhanced chemical vapor deposition (RF-PECVD) technique and were functionalized through exposure to xenon difluoride (XeF2) gas. An atomic force microscopy technique, PeakForce Quantitative Nanomechanical Mapping (QNM®), was used to measure the mechanical properties of the VG sheets. We show that fluorination can significantly enhance the reduced modulus of surfaces comprised of VG sheets. Samples with only ∼3.5% fluorine had a reduced modulus approximately eight times higher than unfunctionalized VG sheets, which is attributed to sp2 to sp3 conversion and a change of the C–C bond length after functionalization. Fluorination also decreased the energy dissipation of the VG sheets and reduced their adhesion to the AFM tip. This method represents a unique approach towards modification of the mechanical properties of nanostructures without a significant increase in weight or change of the VG sheet morphology.

We demonstrate a method for imaging unstained DNA nanostructures with transmission electron microscopy via suspended graphene supports. Central to the technique is a sacrificial silicon membrane beneath the graphene that provides mechanical support during aqueous sample deposition but is then eliminated in a final step using a XeF2 dry etch.